The present invention relates to a process for producing a resin having carbonate bonding with no acidic component in pellets or molding products, all with excellent tone. More particularly, it relates to a process for producing a resin having carbonate bonding by using methylene chloride as an organic solvent and phosgene as a starting material, wherein the polymerization is conducted such that the concentration of carbon tetrachloride (CCl.sub.4) in the phosgene and methylene chloride in the polymerization system satisfies the following equation: EQU A+5B.degree.200,
wherein A represents the CCl.sub.4 concentration in phosgene (ppm) and B represents the CCl.sub.4 concentration in methylene chloride (ppm).
Phosgene usually contains from 250 ppm to 2000 ppm of carbon tetrachloride (CCl.sub.4) as disclosed in Japanese Patent Publication No. 55-14044 (1980).
When producing a polymer using phosgene containing such CCl.sub.4 as starting material and using methylene chloride as a solvent, most of CCl.sub.4 is dissolved in methylene chloride and, as a result, contained in the the methylene chloride solution of the polymer.
CCl.sub.4 remaining in the polymer solution is distributed between the polymer and the methylene chloride at a ratio corresponding to the separation condition upon separating the polymer and methylene chloride.
Usually, methylene chloride thus separated is used again without separating the CCl.sub.4 in industrial recyclic processes. Accordingly, the CCl.sub.4 concentration in methylene chloride increases as the number of recyclizations is increased. From polymers containing such a halogen compound, acidic components originate upon heating, especially in pelletization and molding, thereby causing a problem of corrosion of the dies in molding machines (the die is corroded during the operation of the molding machine) as disclosed in Japanese Patent Application Laying Open (KOKAI) No. 60-81245 (1985). In this case, mold-die corrosion is prevented by blending a specific ester in with the molding composition.
Further, the quality of the polymer is not quite satisfactory e.g., the tone of pellets or molding pieces is worsened depending on the kind of heat stabilizers used for if an insufficient amount of a heat stabilizers is added. However, it has not yet been recognized at all that this drawback is caused by carbon tetrachloride (CCl.sub.4) in the starting phosgene and methylene chloride.
The present inventors have made various studies for preventing the formation of the acidic component upon pelletization and molding of the resultant pellets, as well as for improving the tone of the pellets or molding pieces and, as a result, it has been found that the material mainly contributing to such undesired effects is CCl.sub.4 contained in the methylene chloride solution of the polymer, and have derived the present invention based on the finding that a resin having carbonate bonding of excellent quality, generating no acidic components upon pelletization or molding and having favorable tone of pellets and molding pieces can be produced by reducing the CCl.sub.4 concentration in the starting phosgene and methylene chloride to below a value as shown by the following formula: EQU A+5B.ltoreq.200
wherein A represents the CCl.sub.4 concentration in the phosgene (ppm), and B represents the CCl.sub.4 concentration in the methylene chloride (ppm).
That is, one object of the present invention is to provide a resin having carbonate bonding of excellent quality and this object can be attained by adjusting the CCl.sub.4 concentration (ppm) in the phosgene and the methylene chloride in the polymerization system so as to satisfy the above-mentioned formula.